Simple compressor limiter

Simple compressor limiter

Some years ago I designed a peak limiter to achieve more speech power when using single side band transmission, at the time National Semiconductors made a compressor IC that allowed to adjust the centre frequency thus where the compression took place.

This value of C was such that it accommodated the frequency range of 300 Hz to 3000Hz with acceptable linearity.

I used this to alter the operation of the device to act as a peak limiter to those frequencies that have no value to the intelligence of an audio signal, but push the Peak Envelope Power to the maximum limit of the transmitter.

I chose a value for C that had a centre frequency around 2 KHz, where the gain above this centre frequency was reduced, allowing more microphone gain, boosting the wanted frequencies.
This worked well in the SSB modes but not so good on things that required full spectral response from 300Hz to 3KHz.

I revisited the concept and looked for what was available to do something similar to what I did years ago.

I found the SSM2165, this device incorporates both compression and peak limiting, what I liked about is that a simple circuit provides excellent audio gain with very linear response, making it suitable as a dynamic microphone preamp, incorporating a compressor with variable ratio from 0 to 15:1 plus peak limiting.

An ideal solution for both SSB, AM and FM or any other mode where audio levels require controlling (EchoLink as an example).

The circuit diagram above is very much straight out of the application notes for the device.